The present invention relates to the field of organic synthesis and concerns, in particular, an improved process for the preparation of 15-pentadecanolide. The latter is lactone well-appreciated in perfumery for its musky odor.
It is known from the prior art [see, for example, patent FR 70 19709 or patents U.S. Pat. Nos. 3,907,831 and 3,890,353]to prepare 15-pentadecanolide and some of its derivatives by means of a thermolysis of a peroxide of formula R'.sup.1 --O--O--R'.sup.2, R'.sup.1 represent a group of formula ##STR1## and R'.sup.2 represents a hydrogen, a hydrocarbon, an acyl group or a second group of the above-cited formula. In the latter R'.sup.3 and R'.sup.4 stand for hydrogen, or one of these symbols represents a methyl radical and the other hydrogen, and n stands for an integer of value 0 to 3. As described in the cited prior art, said thermolysis is carried out in an organic solvent at a temperature comprised between 80.degree. and 150.degree. C. and is followed by hydrogenation of the resulting reaction product. Amongst the peroxides used as starting products in the cited process, there is described bis-(13-oxbicyclo[10.4.0]hexadec-12-yl)peroxide. As the medium in which the thermolysis is carried out, there are described, in the prior art documents, solvents which have a boiling point falling in the range of temperatures comprised between 80.degree. and 150.degree.. Liquid aromatic hydrocarbons, such as toluene, xylene and mixtures of o-, m- and p-xylene, are cited as preferred solvents and all the described examples cite xylene as the solvent used. The reaction product, after distillation, consisted of a mixture rich in 15-pentadecanolide. This mixture was then systematically hydrogenated to yield 15-pentadecanolide which was thus freed of its unsaturated homologue, i.e. 15-pentadec-11(12)-enolide.
One of the disadvantages of this prior art process was the fact that the yield of the thermolysis reaction in the mixture of lactones, measured relative to the starting peroxide, was never above 60% and was often below this value. Another disadvantage resided in the fact that 15-pentadecanolide, obtained by hydrogenation of the mixture of lactones, was accompanied of by-products whose separation was laborious and expensive, thus entailing additional costs and reducing the industrial usefulness of the process.